4076
isomerized thermally to trans-IVa at room temperature. The thermal stability of cis-IIIa and -1Va was found to be concentration dependent. They were relatively stable when formed by irradiation at room temperature in alcoholic solvents in 10-4 M (ti,2 24 hr). The uv spectrum of the photostationary mixture of IVa was similar to that obtained by dilution of the concentrated solution irradiated in the nmr tube to the photostationary state at -60". The uv spectrum of cis-IVa" was determined from the photoequilibrium composition and the isosbestic point for cis + trans thermal isomerization. The ratio of cis- and trans-IVa at the photostationary state is very different from the ratio of cis- and trans-IVb formed at the end of the photocyclization reaction. For this reason the quantum yields of the photoreactions for each isomer were determined at 23" (IO-* M ) and are reported in Table I. From the quantum yields
-
Table I. Quantum Yields for Products at 23" = Reaction
Solvent
tJ
Isopropyl alcohol Methanol Methanol Methanol Methanol
0.26 0.016
The trans-Ib thermal cleavage to cis- and trans-Ia is clearly in accordance with the predictions of the orbital symmetry rules. The observed stereospecificity in the nitrone photocyclization is consistent with the symmetry of the nitrone antibonding molecular orbital. As the carbon-oxygen u bond forms in disrotatory motion, the nitrogen T orbital rehybridizes to a lonepair sp3-hybridized orbital in the opposite direction, giving an oxaziridine with the same configuration as the initial nitrone.
Janet S. Splitter,* Tah-Mun Su, Howard Ono, Melvin Calvin Department of Chemistry and Laboratory of Chemical Biodynamics Universiry of California, Berkeley, California 94720 Received June 7, 1971
~
-. -.
trans-Ia -+ trans-Ib trans-IVa IVbb trans-IVa cis-IVac cis-IVa -,trans-IVad cis-IVa + IVbb
0.18 0.46
0.087
1,3-Halogen Shifts Occurring via Four-Membered Ring Halonium Ion Intermediates in the Solvolyses of 3-Halo-1-butyl Trifluoromethanesulfonates
Sir:
Wavelength, 366 nm; concentration, lW4 M ; ferrioxalate The trifluoroacetolysis of primary sulfonate-secactinometry. * Determined by decrease in optical density at 327 ondary halides has proved' t o be an especially adnm, isosbestic point of the nitrone isomers. Determined by change in ratio of optical density at 357 and 317 nm. Calculated vantageous reaction for observing halogen shifts prefrom the photostationary state relation, +.,ctXt" = @C.+t~oXom, sumed to result from ring opening of halonium ion where Xtmand Xcmare the mole fractions of the isomers at photointermediates (eq 1). According to our analysis of the equilibrium. a
0
of formation of trans- and cis-IVa12 and of IVb formation from cis- and trans-IVa, the calculated ratio of IVb isomers formed after the photostationary state was reached, assuming stereospecificity, is 68 cis :32 % trans. After the IVa photostationary state was reached on irradiation at -60", the ratio of IVb isomers found by nmr was 7 1 % cis: 29 % trans. Therefore, these results indicate stereospecificity in the nitrone photocyclization reaction. For the reverse thermal cleavage of oxaziridine to nitrone, Ib in C D 3 0 D gave a 50:50 mixture of cis- and trans-Ia with a first-order rate constant, 6.8 X sec- at - 8 O , by nmr spectroscopy. l 3 The first-order rate constant for cis- -+ trans-Ia under these conditions was 2.9 X 10-5 sec-I at 23". Only in alcoholic solvents was the rate of the thermal cis- -+ trans-Ia isomerization slower than the rate of the Ib ring-opening reaction. l 4 The photostationary state composition of Ia was confirmed to be 100% trans-Ia. (11) trans-IVa: ": : :A 338 nm ( E 14,800). cis-IVa: Ag": 325 nm (e 13,750). Although the uv of the IIIa photostationary state was similar to that of IVa, the photostationary state composition could not be determined because of the lesser solubility of IIIa in CDsOD. (12) The combined 4t+, and &+t suggest, in addition to oxaziridine formation, the efficient formation of a common twisted state analogous to the twisted state in the stilbene direct photoisomerization: (a) D. Gegiou, K. A. Muszkat, and E. Fischer, J . Amer. Chem. Soc., 90,3907 (1968); (b) J. Saltiel and E. D. Megarity, ibid., 91, 1265 (1969); 90, 4759 (1968). (13) trans-Ia: a-CH, T 2.19; NCHa, 7 6.27. cis-la: a-CH, 7 1.94; NCH3, T 6.15. No cis-Ia was detected in the partial irradiation of trans-Ia. (14) At 23" in isopropyl alcohol (10-4 M) the ring cleavage rate was 3.4 x 10-4 sec-1: the cis- trans-Ia thermal rate was 4.0 X 10-7 sec-l. -+
Journal of the American Chemical Society
93:16
I
1
X' 3
products and rates of p-nitrobenzenesulfonate solvolyses (eq 1, R = p-NO2C6H4),1,2, 1,4, and 1,5 participations predominate over competing normal solvolyses by the ratios (k,/k,) 2000, 760, and 7.1, respectively. In contrast with the postulated intermediacy in these reactions of halonium ions consisting of three-, five-, and six-membered rings, evidence was lacking for formation of a four-membered chloronium ion ring. We now report that the 1,3-halogen shift occurs in the trifluoromethanesulfonates 1 (n = 1, R = C F B ) . ~Participation tendencies decrease in the sequence I > Br > C1, the amount of C1 shift being no more than a few per cent. These results complement those of Reineke and McCarthy,3 who have reported a 1,3-bromine migration (1) (a) P. E. Peterson and J. F. Coffey. Tetrahedron Lett., 3131 (1968); (b) J. F. Coffey, Ph.D. Thesis, St. Louis University, 1969; P. E. Peterson and J. F. Coffey, J. Amer. Chem. SOC.,in press; (c) see G. A. Olah and P. E. Peterson, ibid., 90, 4675 (1968), for references to observation by nmr to three-membered and five-membered ring halonium ions. (2) For applications of the enhanced reactivity of triflates see T. M. Su, W. F. Sliwinski, and P. Schleyer, ibid., 91, 5386 (1969), and references cited therein. (3) C. E. Reineke and J . R. McCarthy, Jr., ibid., 92, 6376 (1970).
August 11, I971
4077
during a deamination of 3-bromo-2,2-bis(bromomethyl)-l-&-propylamine perchlorate. A four-membered ring halonium ion intermediate has been postulated in the bromination of a substituted bicyclo[2.2.1]heptane4" and in the bromination of bicyclo[2.1 .O]~entene.~~ Our results for the trifluoroacetolysis of 0.1 M bromotriflate at 60" in the presence of 0.125 M sodium trifluoroacetate are summarized in eq 2. Also given are relative mole per cent yields, estimated by analysis of time-averaged nmr spectra at 100 MHz of the trifluoroacetic acid solution from solvolysis of 0.1 M triflate. Analysis of distilled material (58 yield) gave similar results (eq 2). In addition to the formation of 55 % 1,30
--fO-T-CF3 Br
I
OzCzF, --+
9+ Br 5,55%
0
4
the reaction mixture before or after extraction into CC14 surprisingly indicated the presence of a tentatively identified rearranged component 12, in addition to the expected product of iodine shift, 10. The relative mole per cents (nmr analysis) of 10, 12, and 11 were 58, 36, and 6, respectively. A reference sample of 11 was 0
i
I
I
A
U
10
9
2dLO~C,F, I
+ 6,3376
Br 7,12%
halogen shifted product, the presence in the product of substantial amounts of 1,3-dibroniobutane (7) was of interest as an unanticipated result. The "disproportionation product" 1,3-butanediol bistrifluoroacetate was shown to be absent. The relative yield of 7 was shown to be independent of the per cent reaction and of the initial concentration of 4. These observations rule out formation of 7 uia the dialkylhalonium ion 8. Pre-
Br 8
sumably, therefore, 7 is derived from the reaction of 4 with bromide ions in the solution. Bromide ions may result from elimination in 4 to give highly reactive allylic bromide or, less likely, cia the 1,3 cleavage of 4 or cycloreversion of the intermediate halonium ion (suggested by the results of ref 3). The absence of the anticipated products of p cleavage3 or cycloreversion3 of the halonium ion intermediate, ethylene bromide, and acetaldehyde, serve to support the first alternative for the formation of 7. Acetaldehyde was stable under the reaction conditions and detectable by nmr at a concentration equivalent t o a 2 % yield. In support of the postulated origin of dibromide 7, triflate 4 reacted rapidly with tetraethylammonium bromide in trifluoroacetic acid-sodium trifluoroacetate t o give 7. Furthermore, the dibromide 7 was stable under the conditions of solvolysis of triflate 4. For the reaction of 4, ttl, was approximately 4 hr. Identification of 6 and 7 was accomplished by glc and nmr analysis, using authentic samples. The reaction of 3-iodo- 1-butyl triflate showed qualitative evidence of modest rate enhancement (tl/l approximately 20 min, 60"). Nmr analysis (100 MHz) of (4) (a) M. M. Avram, I. Pogany, F. Badea, I. G. Dinulescu, and C. D. Nenitzescu, Tetrahedron Lett.. 3851 (1969); (b) R. T. Lalonde, J . Amer. Chem. SOC.,87, 4217 (1965).
+-
4.4-4.5, m
-
1.00,t
4.89, q
)3,3sd
(3)
I
12, q = quintet
11, s =sextet
available, but identification of 10 and 12 was based on the clean multiplets observed in early and late platinum spinning band distillation fractions (yield of distillate, 38%), exhibiting increased proportions of 12 and 10, respectively. (Cf. nmr data, eq 3.) Gas chromatography of the distillate using stainless steel columns failed. Tentatively, the formation of 12 is ascribed to the rearrangement shown in eq 4.5 + (4) 13
14
The time-averaged nmr spectrum (100 MHz) of the products of solvolysis of 3-chloro-1-butyl triflate indicated the presence of only approximately 5 of primary chlorides, possibly a mixture of compounds analogous t o 5 and 7. According to the results we have given, the relative halogen reactivity in 1,3 participation is intermediate between that for 1,2 participation (I >> Br >> C1)6 and that for 1,4 participation (I 2 Br 2 Cl).' Acknowledgment. We wish to acknowledge support of this research by the National Science Foundation, Grant No. GP 10919. We are indebted to Dr. R. L. Hansen, 3M Company, for a gift of trifluoromethanesulfonic acid. ( 5 ) For a related case see ref IC. ( 6 ) (a) S.Winstein, E. Grunwald, and L. L. Iiigraham, J . Amer. Chem. SOC.,70, 821 (1948); (b) E. Grunwald, ibid., 73, 5458 (1951). (7) For references see (a) P. E. Peterson, R. J. Bopp, and M. M. Ajo, ibid., 92, 2834 (1970); (b) P. E. Peterson, Accounts Chem. Res., in press. (8) (a) Address correspondence to this author after Sept 1, 1971 at: Department of Chemistry, University of South Carolina, Columbia, S.C. 29208. (b) A. B., June 1971.
Paul E. Peterson,**aWalter F. Boronab Department of Chemistry, St. Louis University St. Louis, Missouri 63156 Received August 14, 1970
Synthesis and Decarbonylation of Pyruvoylpentacarbonylmanganese Sir: The carbonylation of CH3Mn(C0)5 to give CH3COMn(CO)a has been extensively studied la2 and shown (1) K. Noack and F. Calderazzo, J . Organomefal. Chem., 10, 101 (1967). (2) K. Noack, M. Ruch, and F. Calderazzo, Inorg. Chem., 7, 345 (1968), and references therein.
Communications to the Editor
